I would start with the 1/8x1/8....put up a sheet then peel it back to check for reasonably complete coverage...probably the same one you used with the Kerdi.

I thought that Ditra required 2x2" as the smallest recommended tile. Any thing smaller isn't fully supported within the Ditra pattern. I looked up this on Google. But I can't post the link, due to GW obstructs the link. So type in "Schluter ditra and small tiles john bridge" and see if this will take you to an archived thread about this topic.

Thank you StoneTech, I do have that size trowel so that is what I'll try first.

Nice catch enduring, tytyty...luckily haven't purchased or put down Ditra yet...phew!